AP Biology Viral Structure and Genetics

Genetic information is stored in DNA. An RNA transcript can be made and transported into the cytoplasm, where it translated into proteins. RNA comes in three forms: messenger (mRNA), ribosomal (rRNA), and transfer (tRNA). Transcription takes place in three parts: initiation, elongation, and termination. Translation builds an amino acid sequence based on the genetic code. Start and end points are indicated using codons. Silent mutations can occur where the same proteins are translated even though the genetic code has changed as redundancy is built into the genetic code. The second type is missense mutation, where a different amino acid will be added to a protein chain based on the genetic mutation. Nonsense mutations form a stop codon. Natural errors, chemicals, excessive sunlight, and radiation can all cause mutations.

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This might be alitte off topic but for the retrovirus, being part of the host cell's genome and using it's machinery I would assume that it will become dependent on the rate of the host cell's mitotic cycle (cells that reproduce more rapidly will favor the retrovirus) as well. With that in mind, I have also read that some cancers can be caused by viruses. It would make sense then that maybe some viruses have ways of hijacking a cells growth regulation genes maybe???? If it can get an otherwise slow growing cell to start reproducing uncontrollably then it will be able to replicate rapidly as well. Not sure if I'm way off or not.

1 answer

Last reply by: Dr Carleen EatonSun Apr 17, 2011 5:00 PM

Post by Billy Jayon April 12, 2011

I'm having trouble trying to figure out how ssRNA containing viruses transcribe themselves.

(-) RNA strand is transcribed via (RNA-dep-RNA pol) Replicase. This produces the (+) sense-RNA strand, which is then used to translate into proteins. In addition, the (+) strand, which was synthesized using Replicase, is again used as a template to create more (-) RNA strands. These (-) RNA strands are then packaged into the viral capsid.

Viral Structure and Genetics

Viruses
consist of nucleic acid enclosed in a protein capsid. Some viruses
are covered by an envelope derived from the host cell membrane.

Viruses
cannot reproduce independently. To reproduce, they must infect a
host cell and use the host cell's machinery to produce viral
nucleic acids and proteins.

Phage
may reproduce either via the lytic cycle or the lysogenic cycle.

During
the lytic cycle, the virus attaches to the host cell and then
injects its genetic material. A viral enzyme degrades the host DNA
and the host cell's machinery is used to synthesize viral nucleic
acids and proteins. The phage self-assemble and the bacterial cell
is lysed to release the newly produced phage.

During
the lysogenic cycle, phage DNA integrates into the bacterial genome
and is replicated along with the bacterial DNA. An environmental
cue, such as UV light, can trigger the phage to be excised from host
DNA and enter the lytic cycle.

Positive
sense RNA viruses contain RNA that can be translated directly into a
protein. Negative sense RNA viruses contain RNA that serves as a
template for the synthesis of mRNA.

Retroviruses
synthesize complementary DNA (cDNA) from an RNA template using the
enzyme reverse transcriptase. HIV is a retrovirus.

Viral Structure and Genetics

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